Air purification system using ultraviolet light emitting diodes and photocatalyst-coated supports

ABSTRACT

An air cleaning system may provide effective and evenly distributed removal of organic contaminants from airflow. An ultraviolet light emitting diode (UV LED) source may emit ultraviolet light onto a photocatalyst on a support in airflow where airflow is between the UV LED source and the photocatalyst.

BACKGROUND OF THE INVENTION

The present invention generally relates to air purification systems, and more particularly, to an air purification system using ultraviolet light emitting diodes (LED) and photocatalyst-coated supports.

The use of recirculated air may be common within inhabited enclosures. In some cases, airflow may be necessarily recirculated to provide breathable air where air external to the enclosure may not be viable. In other cases, it may be more economical to use recirculated air which has already been adjusted to the correct temperature and humidity. For example, pressurized cabins in aircraft may commonly recirculate a portion of the air rather than try to circulate only external air into the cabin. One result of using recirculated air is that organic contaminants may increase in concentration and may be passed to the inhabitants of the cabin.

One approach to removing contaminants from airflow is to use a photocatalytic air cleaner on airflow. It may be known to use for example, mercury vapor lamps to irradiate a photocatalyst in contact with airflow. Lamps may produce a heterogeneously distributed intensity across a photocatalyst. This may result in portions of the airflow which are less well treated, and still contain contaminants. Mercury vapor lamps may also be commonly made of glass or quartz, and, therefore not useful in environments where mechanical shock might result in their shattering. In addition, the use of lamps may result in insufficient energy absorption by the photocatalyst to provide effective catalysis. This can occur if the emission spectrum of the lamps does not overlap with the absorption spectrum of the photocatalyst.

In some purification systems, titanium dioxide based photocatalysts may be employed. The absorbance of titanium dioxide for photocatalysis drops rapidly with increasing wavelength, and is negligible above 410 nanometers. At wavelengths at which the photocatalyst does not absorb light, no reaction will occur, so use of a light source whose emittance spectrum overlaps poorly with the absorption spectrum of the photocatalyst can result in poor efficiency. It may be desirable to operate a photocatalytic device using a light source which has a wavelength higher than that normally absorbed by titanium dioxide. In some cases, the absorbance spectrum of titanium dioxide may be shifted to higher wavelengths by, for example, doping titanium dioxide with nitrogen or carbon. The effectiveness of titanium based photocatalysts may be short lived as the doped element may degrade quickly and the titanium dioxide is again ineffective at wavelengths above 410 nm.

As can be seen, there is a need for an air cleaning system that may provide efficient and evenly distributed photocatalysis in airflow.

SUMMARY OF THE INVENTION

In one aspect of the present invention, an air cleaning system comprises an ultraviolet light emitting diode (UV LED); a support disposed proximate to the UV LED; and a photocatalyst on the support disposed to contact airflow passing across or through the support, wherein: airflow is between the UV LED and the photocatalyst and, the UV LED is positioned to emit ultraviolet light onto the photocatalyst.

In another aspect of the present invention, an air cleaning system comprises a chamber; an ultraviolet light emitting diode (UV LED) positioned to emit ultraviolet light into the chamber; a plurality of support plates in the chamber spaced parallel to one another, wherein at least one of the plates is disposed proximate the UV LED; and a photocatalyst on the support plates disposed to contact airflow passing across or between the support plates, wherein the UV LED is positioned to emit ultraviolet light onto the photocatalyst.

In yet another aspect of the present invention, a method of purifying airflow comprises passing the airflow through a reactor including an ultraviolet light reactive photocatalyst; emitting ultraviolet light from an ultraviolet light emitting diode into the airflow and onto the photocatalyst; and removing organic contaminants from the airflow that makes contact with the photocatalyst while the ultraviolet light is emitted on the photocatalyst.

These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a plot showing the absorbance spectrum of titanium dioxide between 250 nm and 800 nm wavelengths;

FIG. 1B is a plot showing the emission spectra of a UV LED compared to that for a mercury vapor lamp;

FIG. 2 is a block diagram of an air cleaning system in accordance with an exemplary embodiment of the present invention;

FIG. 3 is a perspective side view of an air cleaning system in accordance with another exemplary embodiment of the present invention;

FIG. 3A is a perspective side view of a support plate of the air cleaning system of FIG. 3;

FIG. 3B is a partial enlarged view of the circle 3B in FIG. 3A; and

FIG. 4 is an exemplary series of steps in a method of removing organic contaminants from airflow in accordance with another exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description is of the best currently contemplated modes of carrying out the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims.

Various inventive features are described below that can each be used independently of one another or in combination with other features. However, any single inventive feature may not address any of the problems discussed above or may only address one of the problems discussed above. Further, one or more of the problems discussed above may not be fully addressed by any of the features described below.

The present invention generally provides an air cleaning system that removes organic contaminants from airflow. Exemplary embodiments of the present invention may be used, for example, in enclosed quarters where airflow may be recirculated and individuals may be subjected to breathing in air that aggregates organic contaminants.

In one aspect, exemplary embodiments of the present invention may use, for example, titanium dioxide as a photocatalyst irradiated with ultraviolet light (UV). The ultraviolet light source employed may be a light emitting diode (LED) whose emission wavelength is centered approximately near 400 nm. As may be seen in FIG. 1A, the absorbance spectrum of titanium dioxide at about 400 nm may be relatively low (approximately 0.15 absorbance) compared to wavelengths of 350 nm or less; just 50 nm difference (approximately 0.9 absorbance). Referring to FIG. 1B, a comparison between the wavelength distribution for a mercury vapor lamp to an UV LED (shaded) is shown. Mercury vapor lamps (which may be currently used for photocatalysis) may have an emission spectrum which overlaps most of the absorption spectrum of titanium dioxide; approximately 255 nm to 430 nm. The UV LED emission spectrum may overlap only a portion of the absorption spectrum of titanium dioxide; approximately 380 nm to 430 nm. The peak intensity for the emission spectrum of the UV LED is centered at approximately 410 nm, near the lower end of absorption spectrum for titanium dioxide. One ordinarily skilled in the art may conclude from the mismatch between the emission spectrum of the LED and the absorption spectrum of titanium dioxide that a photocatalytic reaction using titanium dioxide may not be effective. As a result, photocatalytic reactions are normally carried out using light sources which provide lower wavelengths, such as a mercury vapor lamp. Nonetheless, exemplary embodiments disclosed herein, using a photocatalytic reactor employing a UV LED with this emission spectrum and titanium dioxide as a photocatalyst may be highly effective.

Referring to FIG. 2, an air cleaning system 100 is shown according to an exemplary embodiment of the present invention. FIG. 2 shows the air cleaning system 100 represented as a block diagram showing airflow relative to ultraviolet light emission. The air cleaning system 100 may include an ultraviolet UV light source 110, such as an ultraviolet light emitting diode (UV-LED) and a photocatalyst 170. Quartz windows 105 may be between the UV light source 110 and the photocatalyst 170 and between the photocatalyst 170 and a light meter 109. The light meter 109 may be used in embodiments monitoring the light output from the UV light source 110. A reactor 180 including the photocatalyst 170 may be inside a chamber 115. The photocatalyst 170 may be positioned in the airflow so that organic contaminants (not shown) in the airflow make contact with the photocatalyst 170 in the reactor 180. The UV light source 110 may be positioned to emit ultraviolet light onto the photocatalyst 170 to produce a reaction between the photocatalyst 170 and the organic contaminants (not shown) in the airflow, absorbing the organic contaminants and removing them from airflow.

Referring now to FIGS. 3 and 3A, the air cleaning system 100 is shown with greater detail in accordance with an exemplary embodiment of the present invention. The chamber 115 may be disposed within airflow so that the airflow passes through an entrance end 130 and out an egress end 140. The reactor 180 may be positioned between the entrance end 130 and the egress end 140. The reactor 180 may include a support 120 holding the photocatalyst 170. In an exemplary embodiment, the support 120 may be a plate. The support 120 may sometimes be referred to as a plate(s) 120 or as support plate(s) 120 in the following description. The photocatalyst 170 may be placed on a surface 125 of the support 120. For sake of illustration, only one surface 125 is shown, however, it will be understood that the photocatalyst 170 may be attached to both sides (surfaces) of the support 120. The support 120 may be positioned in the chamber 115, orthogonal to airflow so that airflow passes across the surface 125.

In one exemplary embodiment, the reactor 180 may include a plurality of the support plates 120 supported by the chamber 115. The plates 120 (shown as plates 120 a, 120 b, 120 c, and 120 d) may be spaced parallel from one another. In one aspect, spacing of the plates 120 and the air velocity there through can be adjusted to ensure adequate contact between the air and the photocatalyst 170. In an exemplary embodiment, the plates 120 may include one or more perforations 160. The perforations 160 may be arranged as a set 165. It may be appreciated that some airflow passing over surface 125 of a support plate 120 may pass through one of the perforations 160 and flow along the underside (not shown) of the plate 120 making contact with photocatalyst 170 on said underside. While the support 120 is shown as a plate, other exemplary embodiments may use supports 120 which are not flat. For example, the support 120 may be corrugated to enhance air mixing.

It may also be appreciated that there may be a tradeoff between the size and number of perforations 160 in plates 120 and the amount of surface area available for photocatalytic reaction. The reactor 180 may be configured to optimize irradiation of the photocatalyst 170 on the outermost plates (120 a and 120 d) and underlying plates (120 b and 120 c). In exemplary embodiments where a plurality of support plates 120 are used, the set of perforations 165 of two adjacent support plates 120 may not line up to one another. For example, the set of perforations 165 of plate 120 b may not have centers lined up with the centers of the set of perforations 165 of plate 120 a. Light entering at any angle should at some depth impinge on a catalyst-coated surface. The amount of photocatalytic exposure may be controlled by increasing or decreasing the number of perforations 160 and by increasing or decreasing the number of UV light sources 110.

UV light sources 110 may be positioned to emit ultraviolet light into the chamber 115. The wavelength range of ultraviolet light emitted by the UV light source 110 may be approximately between 200 nm to 435 nm, and depending on the type of photocatalyst 170 used, may be around 385 nm to 410 nm. In an exemplary embodiment, the UV light source 110 may be positioned to provide focused ultraviolet light onto the photocatalyst 170. The support(s) 120 may be supported by the chamber 115 proximate to the UV light source 110 so that the surface 125 holding the photocatalyst 170 is in a plane orthogonal to the UV light source 110. The distance of the photocatalyst 170 from the UV light source 110 may be set so that the beam of ultraviolet light (not shown) remains substantially uniform in coverage and intensity. The UV light source 110 may be approximately 1 inch from the photocatalyst 170 on the outermost plates 120 a and 120 d. It may be appreciated that the use of a UV-LED at such a close distance may provide about 4000 mW/cm² of intensity. Thus, effective catalysis of air contaminants may be achieved within the air cleaning system 100.

In an exemplary embodiment, the UV light source 110 may be one or more UV LEDs. For example, an array 150 of UV LEDs may be employed. In one exemplary embodiment, the UV light source 110 may include an array 150 a on one side 135 of the chamber 115 and an array 150 b on an opposite side 145 of the chamber 115. The arrays 150 a and 150 b may be positioned to emit ultraviolet light orthogonal to airflow, onto the support plate(s) 120 between the two arrays (150 a; 150 b). For example, the array 150 a may be proximate the outermost support plate 120 a while the array 150 b may be proximate the outermost support plate 120 d. The UV light sources 110 may be arranged so that light emitted from adjacent sources may overlap or may irradiate the plates 120 at an angle, thus exposure of the inner plates 120 b and 120 c through the perforations 160 may be achieved.

Referring now to FIG. 3B, an enlarged view of circle 3B from FIG. 3A of a section of the plate 120 is shown. In one exemplary embodiment, the reactor 180 may include a plurality of metallic strips 185 on the plate 120. The strips 185 may include a coating 175 of the photocatalyst 170. The metallic strips 185 may be, for example, aluminum. The photocatalyst 170 may be titanium based, for example, titanium dioxide. In an exemplary embodiment, the reactor 180 may be a mesh 190 of the strips 185 attached to the surface 125 configured to allow airflow to pass over and through strips 185. The mesh 190 may provide higher surface area allowing for increased contact of airflow to the coating 175. It may be appreciated that it is advantageous that the Reynolds number for airflow through the reactor 180, and in particular, in contact with the photocatalyst 170 be high enough that flow is nonlaminar.

Referring now to FIG. 4, a method 400 is shown in accordance with an exemplary embodiment of the present invention. In step 410, airflow may be passed through a reactor. An ultraviolet light reactive photocatalyst may be attached to the support. In step 420, ultraviolet light may be emitted from an ultraviolet light emitting diode into the airflow and focused onto the photocatalyst. The ultraviolet light may irradiate the photocatalyst orthogonal to the direction of airflow. In step 430, organic contaminants may be removed from airflow that makes contact with the photocatalyst while the ultraviolet light is emitted on the photocatalyst.

It should be understood, of course, that the foregoing relates to exemplary embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims. 

We claim:
 1. An air cleaning system, comprising: an ultraviolet light emitting diode (UV-LED); a support disposed proximate to the UV LED; and a photocatalyst on the support disposed to contact airflow passing across or through the support, wherein: airflow is between the UV LED and the photocatalyst and, the UV LED is positioned to emit ultraviolet light onto the photocatalyst.
 2. The air cleaning system of claim 1, further comprising an array of UV LEDs.
 3. The air cleaning system of claim 1, further comprising a chamber, wherein the support is supported by the chamber so that a surface of the support holding the photocatalyst is in a plane orthogonal to the UV LED.
 4. The air cleaning system of claim 3, wherein the chamber includes an entrance for the airflow configured to pass the airflow across the surface of the support in a direction orthogonal to the emitted ultraviolet light.
 5. The air cleaning system of claim 1 wherein the UV LED emits a wavelength around 385 nm to 410 nm.
 6. The air cleaning system of claim 5 wherein the photocatalyst is titanium dioxide based.
 7. An air cleaning system, comprising: a chamber; an ultraviolet light emitting diode (UV-LED) positioned to emit ultraviolet light into the chamber; a plurality of support plates in the chamber spaced parallel to one another, wherein at least one of the plates is disposed proximate the UV LED; and a photocatalyst on the support plates disposed to contact airflow passing across or between the support plates, wherein the UV LED is positioned to emit ultraviolet light onto the photocatalyst.
 8. The air cleaning system of claim 7 further comprising an array of UV LEDs.
 9. The air cleaning system of claim 8 wherein the array of UV LEDs includes a first set of UV LEDs positioned proximate a first outermost support plate and a second set of UV LEDs positioned proximate a second outermost support plate.
 10. The air cleaning system of claim 7 wherein the support plates include sets of perforations disposed within the emitted ultraviolet light and wherein the sets of perforations of two adjacent support plates do not line up to one another.
 11. The air cleaning system of claim 10 further comprising a first set of UV LEDs positioned proximate a first outermost support plate and a second set of UV LEDs positioned proximate a second outermost support plate.
 12. The air cleaning system of claim 11 wherein the chamber includes an entrance for the airflow configured to pass the airflow across the plurality of support plates in a direction orthogonal to the emitted ultraviolet light.
 13. The air cleaning system of claim 11 wherein the first and second sets of UV LEDs are configured to emit the ultraviolet light focused onto the first and second outermost support plates.
 14. The air cleaning system of claim 7 wherein the photocatalyst is coated onto metallic strips.
 15. The air cleaning system of claim 14 wherein the strips form a mesh structure on a surface of the support plates.
 16. The air cleaning system of claim 7 wherein the photocatalyst is titanium dioxide based.
 17. A method of purifying airflow, comprising: passing the airflow through a reactor including an ultraviolet light reactive photocatalyst; emitting ultraviolet light from an ultraviolet light emitting diode into the airflow and onto the photocatalyst; and removing organic contaminants from the airflow that make contact with the photocatalyst while the ultraviolet light is emitted on the photocatalyst.
 18. The method of claim 17 wherein the ultraviolet light is emitted in a range from around 385 nm to 410 nm.
 19. The method of claim 17 wherein the support includes a plurality of support plates spaced parallel to one another, wherein the passing of the airflow through the supports includes the airflow contacting the photocatalyst along at least one surface of each plate.
 20. The method of claim 19 further comprising emitting the ultraviolet light through one or more perforations of at least one of the support plates onto the photocatalyst on an adjacent one of the support plates. 